This invention relates to a frequency multiplying electrical circuit for producing double frequency sine and cosine output signals sin 2x and cos 2x from sine and cosine input signals sin x and cos x.
The invention is particularly well adapted for use in connection with an optical encoder for encoding the position of a rotatable shaft or some other movable member. Such an optical encoder often includes a rotatable code disc having a multiplicity of binary code tracks of successive orders, plus sine and cosine tracks of the next higher order. The tracks are adapted to be read by a reading head comprising one or more light sources and an array of photoelectric transducers or detectors. The reading head has a multiplicity of outputs, which produce digital signals constituting a binary word representing the position of the disc, plus sine and cosine or quadrature output signals which vary sinusoidally as a function of the position of the disc. Typically, the quadrature output signals are of a higher order than the digital output signals. For example, an optical encoder might have eleven binary tracks for producing an 11-bit digital output word, plus sine and cosine tracks of the twelfth order.
The general object of the present invention is to provide a new and improved frequency multiplying electrical circuit for producing double frequency sine and cosine output signals sin 2x and cos 2x from sine and cosine signals sin x and cos x, such as the quadrature output signals of an optical encoder.
The multiplying circuit of the present invention produces one additional output bit or digit, so that the position of the code disc is more precisely represented by the output signals from the optical encoder. Two or more of the multiplying circuits of the present invention may be cascaded to produce two or more additional bits or digits. Thus, for example, sin 4x and cos 4x signals may be produced from the sin 2x and the cos 2x signals. By using two cascaded multiplying circuits, the total number of output tracks can be effectively increased from twelve to fourteen, for example.